In order to investigate the magnetic abnormality influenced by stress in weld seams, experiments on three types of weld seams were carried out and a stress concentration detection instrument – metal magnetic memory (MMM) tester was used. MMM tests on gas pipelines in Puguang initial station in China were conducted and compared MMM wave diagram and mathematical analysis of MMM data and the quantitative MMM characteristics of T weld, straight weld and girth weld. The experiment results showed that different weld seams have different MMM characteristics, types of defects can be identified based on magnetic anomaly signal waveform characteristics and quantitative MMM features which evaluate the pipeline defects quantitatively.

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